1. Field of the Invention
The present invention relates to an image processing apparatus for processing a plurality of color component signals and generating reproduced color image signals.
2. Related Background Art
In a conventional color printer, for example, a technique for preventing degradation of image quality caused by misregistration of color inks when a plurality of primary color inks are overlaid to record an image is known. According to this technique, levels of a plurality of primary color signals are compared, and when they indicate achromatic color levels, only a black ink is colored on a reproduction surface, thereby preventing degradation of image quality.
In particular, in a reading means (e.g., a 3-line CCD sensor) in which a plurality of parallel line sensors are arranged at equal intervals, and an image is focused on these sensors to read an image so as to generate a plurality of color component signals, as shown in FIGS. 12 and 15, the above-mentioned misregistration problem cannot be ignored. Therefore technique for accurately discriminating chromatic/achromatic levels is proposed in, e.g., U.S. patent application Ser. No. 416,587.
This prior art, however, does not take into consideration a difference between spatial frequency gain characteristics inherent to sensors for generating R (red), G (green), and B (blue) color component signals upon discrimination of chromatic and achromatic signals.
For this reason, when the color components are subjected to the same signal processing, a chromatic/achromatic judgment error caused by degradation of an achromatic level cannot be prevented due to a difference between spatial frequency gain characteristics of the R, G, and B sensors.
U.S. patent application Ser. No. 416,587 also proposes a method of correcting offsets of reading positions caused by intervals between adjacent line sensors. According to this method, output signals of a specific pixel group are interpolated to align image signals among pixel groups.
According to the prior art, however, spatial frequency sensitivity characteristics are impaired due to interpolation calculations and characteristics of the apparatus, thus often causing a change in color at a change point (e.g., an edge portion) of an image. For this reason, color misregistration particularly appears at an image edge portion, and image quality of this portion is considerably degraded.
The color misregistration is especially conspicuous in the above-mentioned 3-line CCD sensor.